Biometric electrodes are used in various clinical and biomedical applications for electrically interfacing between examined tissue and monitoring instrumentation. Such biometric electrodes are usually comprised from an adhesive patch having an adhering side (also referred to herein as tissue interfacing face) comprising an electrically conductive surface, and an electrical connector mounted on the other side (also referred to herein as electrically coupling face) of the adhesive patch and electrically coupled to the electrically conductive surface. Electrically conducting wires equipped with mating connectors are used to connect to the electrode and establish electrical connection between the electrically conductive surfaces of the biomedical electrodes and the instruments used for sensing and/or applying electrical signals therethrough.
For example, in electrocardiography (ECG) biometric electrodes attached to the skin over the chest area of a patient are used for sensing electrical signals of the heart (also known as passive electrodes), while in impedance cardiography (ICG) biomedical electrodes are also used to transfer electrical signals to the tissue and sense responsive electrical signals from the tissue contacted by an electrically conductive surface of an electrode (also known as active electrodes).
Design considerations of active electrodes used to apply electrical signals to a contacted tissue usually concentrate on obtaining good electrical contact between the electrically conductive surface of the electrode and the contacted tissue while neglecting patients' discomfort due to the applied electrical signals. There have been some attempts to alleviate patient discomfort associated with the use of biomedical electrodes. For example, U.S. Pat. No. 7,771,419 describes various techniques to distribute the electrical currents applied by the electrode by using an electrode mechanically and electrically divided into multiple metallic electrodes to provide a resistive-capacitive or resistive-inductive voltage divider.
A biomedical electrode is described in U.S. Pat. No. 5,372,125 which is made of a thin flat and flexible material and includes a die-cut patch having a non-conductive adhesive coating applied on one side of the patch, a foundation component formed into four integral functional areas, a conductive component made up of an electrically conductive material with three contiguous portions, and a conductive media.
U.S. Pat. No. 6,415,170 described a biomedical electrode comprising a connector stud anchored in a patch of adhesive-coated backing material used to secure the electrode to the skin of a patient, the connector stud is located in a pierced opening in the backing material and has a head portion to which an electrical lead of an electromedical monitoring/diagnostic system can be attached, and an electrode plate which placed in electrical communication with the skin of the patient.
In WO 2005/099606 there is described a biomedical return electrode for electrosurgery or radiofrequency (RF). The biomedical electrode in this publication comprise a biomedical electrode pad, an electrode conductor for receiving electrical energy from tissue via a return path, and a thermochromic liquid crystal (TLC) layer coupled to the conductor, where the TLC layer is configured to change its colour at one or more sites dependent upon the conductor temperature at each site.
General Description
The present invention relates to a novel biomedical electrode assembly configured and operable to perform an actual measurement mode, as well as a testing mode suitable for testing the electrode condition which may be used to determine whether the electrode is in an acceptable condition for use in a medical procedure, and/or to generate calibrating data usable for calibrating electric signals measured using the electrode assembly.
With regard to the test mode, the following should be understood. In the conventional ECG and ICG applications it is usually assumed that the skin-electrode interface (i.e., the electrical properties of the connection obtained between the electrically conductive surface of the electrode and the contacted tissue) is acceptably good and that the electrically conductive surface of the electrodes is in good functioning condition. However, these conditions cannot always be met, and actually tend to degrade over time. In fact, the conditions of electrically conductive electrodes employing moistening materials (e.g., Hydrogel) for improving the tissue-electrode interface may degrade during continuous use of the electrode, particularly due to lose of moisture and reduced concentrations of electrically conductive minerals (e.g., silver) at the interface area.
For example, gel based electrodes, which tend to dehydrate over time, have specific shelf life terms (e.g., 18 months) after which they are expired and should not be used. In addition, if the unpacked electrodes are not properly maintained (e.g., the electrodes are exposed to direct sunlight or high temperature conditions), or in attempts to reuse the unpacked electrodes, the effectiveness of the electrodes may degrade and affect the signals measured or applied therewith. These problems are particularly relevant to home or mobile medical appliances intended for in-home use, wherein the electrodes may be transported in vehicles to user's houses. The environmental conditions in vehicles are usually not suitable (e.g., high temperature, direct sunlight, dryness) for storing such gel based electrodes, and may substantially shorten their life-cycle.
It is therefore desirous to allow testing and verifying the electrode condition (e.g., quality of the gel used in the electrode and/or presence of electrically conducting ingredients therein), while conventional monitoring instruments and the electrodes used nowadays are incapable of providing the practitioner with indications about the reliability of the used electrodes, as well as with capabilities to evaluate these conditions.
The biomedical electrode assembly of the present invention is configured to be electrically coupled to a skin tissue, whereby it may be operated in an active mode for applying electrical signals to the contacted tissue, or in a sensing mode for sensing electrical signals propagating in the contacted tissue, for determining one or more physiological parameters (e.g., patient's hemodynamics).
The electrode assembly of the present invention in some of its embodiments includes a contact member having a tissue interfacing face, by which it is brought in contact with the skin, and an electrical coupling face, used for electrically coupling the electrode to equipment (e.g., monitoring equipment) suitable for measuring and/or applying electrical signals therewith. In some preferred embodiments of the present invention the biomedical electrode includes an elongated electrically conductive surface (also referred to herein as a main electrode) longitudinally disposed along a surface area on the tissue interfacing face of the contact member.
The use of an electrical conductive surface having an elongated shape advantageously increases the length of the contact area, and thereby improves the tissue-electrode interface. Also, the use of an elongated electrical conductive surface can provide for improving the homogeneity of the applied electrical currents in the contacted tissue by arranging such elongated electrically conductive surface on the tissue interfacing face of the contact member to cause the electrical currents applied to the contacted tissue to propagate therein in a direction substantially perpendicular to the elongated electrically conductive surface of the electrode. Furthermore, using an elongated electrically conductive surface provides for reducing the density of the electrical current applied to the tissue. In this way, patient's discomfort which may occur due to the transmission of electrical currents to the tissue may be alleviated or even prevented.
The electrode assembly may comprise at least two spaced apart connectors disposed on the electrical coupling face of the contact member and electrically coupled to the elongated electrically conductive surface of the electrode assembly. The spaced apart connectors may be configured and operable to connect to at least two mating connectors, to thereby obtain mechanical and electrical connection therewith. With this design the biomedical electrode assembly of the present invention may be used to provide homogenous distribution of electrical currents transferred to the contacted tissue through the electrical conductive surface of the electrode (e.g., due to applied electrical signals) and alleviate patient discomfort which may be caused by the applied electrical currents.
In the testing mode, the biomedical electrode may be used to measure electrical properties of the electrically conductive surface of the electrode itself and thereby enable to test and verify the condition of the electrically conductive surface of the electrode.
For example, the electrically conductive surface of the electrode of the present invention may include an electrically conductive gel medium. For effective measurements, the gel medium should satisfy a certain conditions of humidity and a certain concentration of electrically conducting materials (e.g., salts, and/or other minerals). Such types of electrodes typically suffer from the fact that gel becomes dry over time and that its electrical conductivity properties degrade over time (e.g., due to inadequate maintenance conditions), which should be identified prior to (or during) the use of the electrode assembly, otherwise meaningful measurements might not be performed. Furthermore, the condition of the electrically conductive surface of the electrode may change during a prolonged usage, and also the electrical properties of the skin-electrode interface may introduce interferences (noise) in the electrical signals sensed, or applied, via the electrode.
Calibrating data computed based on electrical properties of the electrically conductive surface measured in the testing mode may be further used to adjust electrical signals sensed, or applied, via the electrode assembly to reduce or eliminate interfering effects, such as noise, which may be introduced during normal use of the electrode.
Thus, in possible embodiments of the present invention a calibration stage may be carried out, before or during, the use of the biomedical electrodes of the present invention for actual measurements on a tissue. In the calibration stage, electrical properties (e.g., electrical resistance or conductivity) of the electrically conductive surface of the electrode are measured, enabling to use such measured data to determine whether the electrode is in an acceptable condition for use in a medical procedure, and/or to generate the calibrating data.
At least one of the at least two connectors mounted on the electrically coupling face may be used to transfer electrical signals (charges), received via the mating connector to which it is connected, to the electrically conductive surface of the biomedical electrode. In the testing mode, at least one other connector of the at least two connectors may be used for sensing electrical currents propagating in the electrically conductive surface of the electrode assembly e.g., via a mating connector to which the at least one other connector is connected, for measuring at least one electrical property of the electrically conductive surface of the electrode.
Advantageously, when operated in the active mode two or more connectors may be used to apply electric signals to the contacted tissue via the electrically conductive surface of the electrode.
In some embodiments of the present invention the contact member includes an additional electrically conductive surface (also referred to herein as additional electrode) disposed spaced apart from the elongated electrode on the tissue interfacing face of the contact member and configured and operable to contact another piece of tissue of the patient. An at least one additional connector, electrically coupled to the additional electrically conducting surface, may be disposed on the electric coupling face of the contact member for establishing electrical and mechanical connection with an additional mating connector.
Therefore, some embodiments of the present invention provide an electrode assembly having a main electrically conductive surface disposed on a surface area of the contact member, and an additional electrically conductive surface disposed spaced apart on a surface area of the contact member. These embodiments of the electrode assembly of the present invention permit operating the electrode assembly in a mixed mode, wherein the main electrically conductive surface of the electrode assembly is used to apply electrical signals to the contacted tissue, while the additional electrically conductive surface of the electrode assembly is used to sense electrical signals propagating in the contacted skin in response to the electrical signals applied.
The main electrically conductive surface is an elongated surface electrically coupled to at least two electrical connectors, as described hereinabove and hereinbelow. The additional electrically conductive surface may have a circular or polygonal shape or any other suitable shape, electrically coupled to one or more additional electrical connectors. Optionally, the additional electrically conductive surface is also an elongated surface having two or more additional spaced apart connectors, as described hereinabove and hereinbelow.
In possible embodiments of the present invention the main and the additional electrically conductive surfaces may be configured to allow operating the electrode assembly of the present invention in a testing mode usable for testing their conditions. Optionally, the additional electrically conductive surface is configured as an elongated surface disposed on the tissue interfacing face of the contact member, spaced apart and in parallel to the main electrically conductive surface. Arranging the elongated main and additional electrically conductive surfaces in parallel causes the electrical currents to propagate in the contacted tissue in a direction substantially perpendicular to the elongated electrically conductive surfaces, which helps to evenly and homogenously distribute the electrical currents in the contacted tissue and thus alleviate or prevent patient discomfort.
The biomedical electrodes of the present invention may be operated by a measurement device configured and operable to test the electrically conductive surface(s) of the electrodes (testing mode), and after verifying that the electrodes are in acceptable operating condition, to apply and/or sense electrical signals (measuring mode) via one or more biomedical electrodes of the present invention that are electrically coupled to a tissue of a subject. In exemplary embodiments of the present invention the measurement device operates to selectively switch between the testing and measuring modes.
In the testing mode, the measurement device operates to apply electrical signals through at least one connector electrically coupled to one of the electrically conductive surfaces of the electrode, and sense electric signals propagating in the tested electrically conductive surface of the electrode via another connector electrically coupled thereto. The measurement device may then analyze the sensed electrical signals and generate data indicative of electrical properties and/or operational condition of the tested electrically conductive surface. The sensed and analyzed electrical signals may be further used to generate calibrating data usable for adjusting electrical signals sensed or applied via the electrode.
In the measurement mode, the measurement device operates to apply and/or sense electrical signals via one or more electrically conductive surfaces coupled to a skin tissue of a subject. For example, if operated in a sensing mode, the measurement device may sense electrical signals propagating in a contacted tissue via a single electrically conductive surface of an electrode assembly of the present invention. In another possible example, the measurement device may be operated in a mixed mode to apply electrical signals through one or more connectors electrically coupled to a main electrically conductive surface, and to sense electrical signals, responsive to the applied signals, via at least one connector electrically coupled to an additional electrically conductive surface. As will be explained and demonstrated hereinbelow, the main and additional electrically conductive surfaces may be disposed on two different contact members of two different electrode assemblies of the present invention, or on a single contact member of the same electrode assembly of this invention.
A connector unit, including two mating connectors may be used to connect the electrode assembly of the present invention to monitoring equipment. The mating connectors in some embodiments are shiftable between engaged state and disengaged state, such that when in their engaged states the connectors grab corresponding connecting elements, and release them when in their disengaged states. The mating connectors may be associated with two respective actuators, each actuator being configured and operable to reversibly change the state of a corresponding connector, to thereby allow the operator to attach the connector unit to the electric connectors mounted on the electrically coupling face of the contact element.
The electrode assembly of the present invention may be a type of patch-electrode or self-adhesive electrode.
There is therefore provided according to one aspect of the present invention a biomedical electrode structure comprising a contact member having a tissue interfacing face for contacting a tissue surface and an opposite electrical coupling face, at least a first electrically conductive surface disposed within said tissue interfacing face and being configured and operable to electrically couple to a portion of the contacted tissue, at least two electrical connectors mounted in a spaced apart relationship on said electrical coupling face and electrically coupled to different regions of said electrically conductive surface for allowing measurement of at least one electrical property (e.g., electrical impedance, resistance or conductivity) of at least a portion of said at least first electrically conductive surface residing therebetween.
In possible embodiments of the present invention the at least first electrically conductive surface is an elongated surface. In this configuration the at least two electrical connectors may be electrically coupled to spaced apart regions of the electrically conductive surface to permit measurement of the at least one electrical property along substantial length of the electrically conductive surface (between these regions). The length of the first electrically conductive surface may generally be in the range of 30 to 60 mm, and its width may generally be in the range of 8 to 16 mm. The electrically conductive surface may have a rectangular (e.g., having an aspect ratio generally in the range of 0.13 to 0.53, oval, polygonal, or any other suitable shape.
In possible embodiments of the present invention the biomedical electrode structure may further comprise an additional second electrically conductive surface disposed on the tissue interfacing face spaced apart from the first electrically conductive surface configured and operable to contact a different portion of the contacted tissue, and at least one additional electric connector electrically coupled to said additional electrical conductive surface. The additional electrically conductive surface may be configured and operable to sense electric signals propagating in the contacted tissue in response to electric signals applied by the at least one electrically conductive surface. Optionally, the additional electrically conductive surface is an elongated surface.
In some embodiments of the present invention the first electrically conductive surface and the second electric conductive surface are configured such that electrical currents passing in the contacted tissue due to the applied electric signals propagate in a direction substantially perpendicular to at least one of said electrically conductive surfaces.
In some applications of the present invention the electrically conductive surfaces of the biomedical electrode structure are disposed on the tissue interfacing surface substantially parallel to each other, such that the electrical currents propagating in contacted tissue residing therebetween are homogenously distributed at least along the length of the contacted tissue.
The distance between the electrical conductive surfaces of the first and second electrically conductive surfaces may generally be in the range of 30 to 60 mm.
In another aspect the present invention is directed to a method for calibrating a biomedical monitoring setup. The method comprises steps of: (i) providing at least one biomedical electrode comprising an electrically conductive surface and at least two spaced apart electrical connectors electrically coupled to the electrically conductive surface; (ii) applying electrical signals to the electrically conductive surface via at least one of the electrical connectors, (iii) measuring responsive electrical signals propagating in the electrically conductive surface via at least one other of the electrical connectors and generating data indicative of the propagating electrical signals; and (iv) analyzing the data and determining at least one electrical property of the electrically conductive surface.
In possible embodiments of the present invention the method may further comprise steps of: (v) issuing an indication whenever the determined at least one electrical property is not acceptable for carrying out the monitoring; and (vi) waiting for replacement of the at least one biomedical electrode. Optionally, steps (i) to (vi) are repeated until determining that the at least one electrical property is acceptable for carrying out the monitoring.
The method may further comprise generating calibrating data indicative of electrical signals to be applied, or of electrical signals sensed, via the electrically conductive surface, based on the at least one electrical property.
According to yet another aspect, the present invention is directed to a measurement device usable for monitoring one or more physiological parameters, and comprising an electrical monitoring unit, at least one connector configured and operable to electrically couple an electrode structure to the electrical monitoring unit via at least two electrical connectors of the electrode structure, a switching circuitry configured and operable to alter connectivity between the electrical monitoring unit and the at least one connector to provide one of the following operating modes:
a testing mode for measuring at least one electrical property of said electrode; and
a monitoring mode for applying electrical signals from said electrical monitoring unit to a tissue contacted by said electrode structure or for sensing via said electrode structure electrical signals propagating in said tissue.
In some embodiments of the present invention the electrical monitoring unit comprises an electrometer and an electrical signal generator.
According to another aspect, the present invention is directed to a connector unit usable for electrically coupling monitoring equipment to an electrode structure comprising two electrical connectors. In some applications the connector unit comprises two electrically conductive latching elements shiftable between engaged and disengaged states, a housing configured to receive two electrically conductive wires and electrically couple each of said wires with a respective latch element, and two actuators movably attached to said housing, configured and operable to change the states of the latching elements between their engaged and disengaged states.
Optionally, the two electrical connectors (also referred herein as connecting elements) of the electrode may be in a form of electrically conducting studs and the latching elements may be configured and operable to embrace said studs in their engaged state.
It is noted that the embodiments exemplified in the figures are not intended to be in scale and are in diagram form to facilitate ease of understanding and description.